Abstract: The effect of activating fluxes on TIG welding of mild steel is studied in this paper.On the bases of analyzing the regulation that affects the penetration and shape of weld,the base component of flux be confirmed.Multi-component compounding is investigated by using ortho-gonal method,thus the influence pattern of the mass fractions of individual components on the penetration is obtained finally.It has marked effect on the penetration when the mass fraction of SiO₂ is 40%.It has distinct effect on the penetration when the mass fraction of TiO₂ and Cr₂O₃ less then 30%.It has distinct effect on the penetration when the mass fraction of halide is on small scale.Considering the appearance of weld,presented activating flux made up of SiO₂,TiO₂,Cr₂O₃ and halide for A-TIG welding of mild steel.So that the optimal compounding can made the penetration deepened by triple,be able to weld through mild steel plate in thickness of 12 mm once and away without groove preparation on the normal welding conditions,appearance of weld is elegant.